Biological Membranes

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Biological Membranes

• Formation of the membrane lead to appearance of
  the first cell.
• Membrane define boundaries of the cell.
• Regulate traffic in and out of the cell.
• Divide internal space into compartments.
• Segregate processes and reactions.

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Biological functions of membranes are derived
from their physical properties.

• Flexible (allow cell growth and movement).
• Self-sealing (allow endo- and exo-cytosis).
• Selectively permeable to polar solutes (can
  retain selectively specific compounds with in
  cells).
• Membranes contain proteins which catalyze various
  cellular processes.

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Membrane architecture.

• Membrane consist of two layers.
• Membranes are two-dimensional.
• Membranes are fluid.

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Lipid composition of different membranes of the
rat hepatocyte.
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Fluid mosaic model
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Structural elements of membranes.
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Asymmetric distribution between inner and outer
monolayer.
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Membranes in motion.
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Organisms adapt their membranes to suit their
needs.
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Membrane proteins diffuse freely in the bilayer.
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Some proteins span the lipid bilayer.
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Proteins that span the bilayer.
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Peripheral and integral proteins.
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Proteins can be covalently attached to the lipids.
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Classification of the integral membrane proteins.
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Sequence of proteins can give clues to their
location.
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Membrane fusion.
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Viral entry through membrane fusion.
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Transport across membranes.

• Simple diffusion. Higher concentration to lower
  concentration.
• Ions of opposite charge separated by membrane,
  create electrical gradient, Vm.
• Direction of movement depends on the chemical and
  electrical gradient.
• Electrochemical gradient of electrochemical
  potential.

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Solute transport across membranes.
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Transmembrane passage.

• Facilitated diffusion or passive transport.
• Transporters and permeases catalyze transport.

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Glucose transporter (passive).
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